Fail-safe lamp filament monitoring circuit

ABSTRACT

This invention relates to a fail-safe lamp filament monitoring circuit including an a.c. signal source to provide an a.c. signal to the primary of a transformer which, in turn, supplies alternating electrical energy to a lamp filament connected in its secondary, a monitoring device responsive to the current in the primary winding and an auxiliary loading device connected in the secondary. The auxiliary loading device is effective to increase power flow through the transformer to energize the filament to a level where the monitoring device is operated and held operated until the lamp filament is no longer energized at which time the monitoring device is released at the transformer magnetizing current.

King

Apr. 2, 1974 FAIL-SAFE LAMP FILAMENT MONITORING CIRCUIT Kenneth GordonKing, London, England The Westinghouse Brake and Signal Company,Limited, London, England Filed: Sept. 22, 1972 Appl. No.: 291,230

Related U.S. Application Data Division of Ser. No. 69,765, Sept. 4,1970, Pat. No. 3,725,728.

Inventor:

Assignee:

Foreign Application Priority Data Sept. 23, 1969 Great Britain 46903/69U.S. Cl 315/136, 315/276, 315/362, 340/251 Int. Cl. H01j 7/42, H05b37/03, G08b 21/00 Field of Search 315/276, 129, 120, 136, 315/362, 127,119; 324/51,20, 22; 340/85, 251; 317/157 References Cited UNITED STATESPATENTS 10 1941 Higgins 315/276 x 1,788,597 l/l93l Schultz 315/362 XPrimary Examiner-James W. Lawrence Assistant Examiner-Marvin NussbaumAttorney, Agent, or Firm-J. B. Sotak; H. A. Williamson [57] ABSTRACTThis invention relates to a fail-safe lamp filament monitoring circuitincluding an a.c. signal source to provide an a.c. signal to the primaryof a transformer which, in turn, supplies alternating electrical energyto a lamp filament connected in its secondary, a monitoring deviceresponsive to the current in the primary winding and an auxiliaryloading device connected in the secondary. The auxiliary loading deviceis effective to increase power flow through the transformer to energizethe filament to a level where the monitoring device is operated and heldoperated until the lamp filament is no longer energized at which timethe monitoring device is released at the transformer magnetizingcurrent.

5 Claims, 2 Drawing Figures V 3.801.860 PATENTEU 2|974 Mg] fZZa/nen /ZIFAIL-SAFE LAMP FILAMENT MONITORING CIRCUIT This application is adivision of my copending application for letters Patent of the UnitedStates, Ser. No. 69,765, filed Sept. 4, 1970, for Fail-Safe LampFilament Monitoring Circuit now US. Pat. No. 3,725,728, issued Apr. 3,I973.

My invention relates to a fail-safe lamp filament monitoring circuit.

More particularly, my invention relates to a fail-safe lamp filamentmonitoring circuit comprising a transformer device, a lamp filament, amonitoring device, and an auxiliary loading circuit. The transformerdevice has a primary and a secondary winding, an a.c. signal sourceproviding an a.c. signal to the primary winding. The lamp filament isconnected to the secondary winding so that the transformer devicesupplies electrical energy to the lamp filament. The monitoring devicehas a first and a second state, and is responsive to the current in theprimary winding of the transformer. It is initially in its second state.The auxiliary loading circuit is also connected to the secondary windingof the transformer and is effective to increase the power flow throughthe transformer device to energize the lamp filament to a preselectedenergizing power flow level which causes the monitoring device to assumeand to be held operated in its first state. The monitoring devicereassumes its second state at a preselected lower current flow level ofthe primary winding of the transformer when the filament is no longerenergized due to full or partial open-circuiting.

In prior arrangements for testing the integrity of lamp filamentcircuits employed in railway signal applications, the filaments wereconnected in the secondary circuit of a transformer and fed withalternating current through the transformer. A current sensing relay wasplaced in the primary circuit of the transformer. It was desirable thatthe current sensing relay have a sensitivity capability such that it washeld by the filament energizing power level and released upon theceasing of the filament power flow. However, it has been found that insuch arrangements the current sensing relay could remain held by themagnetizing current in the transformer primary circuit even in theabsence of filament power flow. This is most unsatisfactory since itcontravenes the fail-safe feature considered essential in railwayenvironment wayside traffic signaling applications.

It is therefore an object of this invention to provide a uniquefail-safe lamp filament monitoring circuit for detecting and indicatingfilament integrity through incorporation of a distinct filamentenergization power level whenever the filament is energized.

Another object of this invention is to provide a new fail-safe lampfilament monitoring circuit which utilizes transformer action to providea preselected reference current power level, which power'level ispresent when filament power flow ceases.

Yet another object of this invention is to provide an improved fail-safelamp filament monitoring circuit having auxiliary loading meansresponsive to the current through the filament to present a distinctfilament energization power level for detection when the filament isenergized.

Still another object of this invention is to provide a novel fail-safelamp filament monitoring circuit having a first and a second filament,the second filament chosen to present the same power level for detectionas the first filament whenever power flow in the first filament ceases.

In the attainment of the foregoing objects a fail-safe lamp filamentmonitoring circuit has been invented which includes an a.c. signalsource to provide an a.c. signal to the primary winding of a transformerfor supplying alternating electrical energy to a lamp filament connectedin the secondary winding of the transformer, a monitoring relayresponsive to the current in the primary winding of the transformer andan auxiliary resistive load device connected in the secondary winding ofthe transformer. The auxiliary resistance load device is effective toincrease the power flow through the transformer to energize the filamentto a level where the monitoring relay is operated and held operateduntil the filament is no longer energized at which time the relay isreleased at the transformer magnetizing current level, or some otherpreselected current level.

The circuit may also include a supplemental filament also connected inthe secondary winding of the transformer and a further relay toselectively energize the first filament at a power level provided by thecombination of the first filament and the auxiliary resistive loaddevice until failure of the first filament whereupon the supplementalfilament is energized, the auxiliary resistive load device drawing powerwhich is substantially equivalent to the difference in power drawn bythe filaments.

Further, the monitoring relay may be responsive to a partial failure ofthe first filament which would reduce the power flow through thetransformer to a level distinguishable from that provided by thetransformer magnetizing current by the flow to the auxiliary resistivedevice.

Other objects and advantages of the present invention will becomeapparent from the ensuing description of illustrative embodimentsthereof, in the course of which reference is had to the accompanyingdrawings in which:

FIG. 1 depicts one preferred embodiment in schematic form of the instantfail-safe filament monitoring circuit in which one lamp filament and anauxiliary resistive load are connected across the transformer secondary.

FIG. 2 depicts still another embodiment of the instant fail-safe lampfilament monitoring circuit in schematic fonn in which a supplementalfilament and a further relay are also connected in the transformersecondary.

A description of the above embodiments will follow and then the novelfeatures of the invention will be presented in the appended claims.

Referring now to the drawings and particularly to FIG. 1 which depictsone preferred embodiment of the present invention, it will be seen inFIG. 1 that a transformer Tl has an a.c. signal provided to its primaryvia a.cv signal source 11. A monitoring means in the form of a relay MRis also connected to the primary winding of transformer T1 and arrangedto indicate, by means of its front contact MR1 and associatedconventional circuitry depicted as a filament integrity indicationcircuit 21, whether or not the current flowing in the primary winding oftransformer T1 is sufficient to pick up contact MRI of relay MR. Asshown in FIG. 1, connected in the secondary of transformer T1 is 'a lamp12 having a filament 13, and an auxiliary loading resistor R,, connectedacross the secondary winding. The amount of current necessary to flowthrough the primary winding to pick up frontcontact MR1 of relay MR isdetermined by the amount of power consumed by resistor R, and filament13 of lamp 12. The value of the resistance R is chosen with due regardto the power consumed in the lamp 12 and the magnetizing current of thetransformer T1, which current initially flows in the primary oftransformer T1, to ensure that while front contact MRI of monitoringrelay MR is picked up and held up by the current flowing to illuminatelamp 12, should such current fall to a level at which illuminationceases through total or partial opencircuiting of the filament 13, thenfront contact MRI of monitoring relay MR is reliably released and thepossibility of contact MRI of relay MR being held up by the primarymagnetizing current is eliminated. Accordingly, as long as filament 13of lamp 12 is conducting, the power level due to power consumed byfilament l3 of lamp 12 and resistor R, will cause the picking up offront contact MRI of monitoring relay MR establishing a first electricalstate and thereby completing a circuit from a B (positive) batteryterminal over front contact MR1 of monitoring relay MR, lead 17 tofilament integrity indication circuit 21, thereby providing anindication of filament energization and, a fortiori, lamp illumination.Should an open circuit be caused in filament 13 of lamp 12, then thepower drawn by the secondary of transformer T1 will be solely due toresistor R the value of which is much greater than the parallelcombination of resistance R and filament resistance. Hence, the currentin the secondary of transformer T1 will be considerably diminished. Itis at this current that contact MRI of relay MR, being chosen such thatit will only be picked up at the predetermined power level required byresistor R and filament 13 of lamp 12, will release and no circuit willbe completed to filament integrity indication circuit 21. Similarly,should resistor R A become open-circuited (noting that in fail-safetheory it is assumed that resistors never short circuit), monitoringrelay MR would assume a second electrical state, namely, release itsfront contact MR1 since the power level at which contact MR1 of relay MRis picked up is no longer present due to the opening of resistor R,,.Further, should either the primary or secondary winding short betweenturns, there would be no transformer action present and, therefore,there would not be present the power level due to resistor R andfilament 13 of lamp 12.

Reference is now made to FIG. 2 which shows still another embodiment ofthe present invention employing a double-filament lamp, the twofilaments of which are positioned and chosen to consume differentpowers. The main filament 13a is the one normally used and is positionedat the optimum optical position in the lamp 12a. A supplemental filament14 is, of necessity, positioned elsewhere within lamp 12a and,therefore, must dissipate a higher power than filament 13a in order tocompensate for the reduced optical efficiency resulting from thefilament displacement from the optimum optical position in the opticalsystem.

As shown in FIG. 2, the filament 13a is energized by the upper portionof the secondary ofa transformer T1 through an auxiliary load controlrelay coil MA. A changeover contact a having front and back portions band c, respectively, is arranged to connect an auxiliary load resistor Racross a portion of the secondary of transformer T1 when in position b,so long as relay MA is energized. On relay MA becoming deenergized thecontact a changes over to position c to connect the supplementalfilament 14 across the lower portion of the secondary of transformer T1,in place of auxiliary load resistor R Once again, a monitoring relay MRis connected to the primary winding of transformer T1 and arranged toindicate by means of its front contact MR1 and associated. circuitrydepicted asa filament integrity indication circuit 21a, whether or notthe current flowing through the primary winding of transformer T1 issufficient to pick up contact MRI of relay MR. In the instant preferredembodiment, the auxiliary load resistor R is chosen with regard to theburden upon relay coil MA and relative power consumption of the twofilaments 13a and 14 of lamp 12a so that the power flow through thetransformer T1 is approximately the same under energization of filament13a as it is under energization of supplemental filament 14.

Also to be considered upon selection of resistor R is differentiationbetweenpower flows from that due to the magnetizing current of theprimary of transformer T1 such that there is no possibility of the frontcontact MR1 of relay MR being held up by magnetizing current flow whendue to complete or partial failure of both filament 13a and supplementalfilament 14, and there is a reduced or no power flow through thetransformer T1. Once again, should resistor R become open-circuited, thefilament 13a is energized and monitoring relay MR would not release itsfront contact MR1 since the power level at which contact MR1 of relay MRis maintained picked up by the lighting of supplemental filament 14 overback contact c of relay MA. Thus, a circuit path through contact b ofrelay MA is no longer present due to the opening of resistor R.-

It will be appreciated that while the invention has been illustrated asemploying a resistive loading device, the invention is suitably adaptedfor any power consuming device.

While the invention hasbeen described with reference to particularembodiments, it is understood that other modifications, changes andvariations may be made by those skilled in the art without departingfrom the spirit of the invention or scope of the claims.

Having thus described my invention, what I claim is:

1. A fail-safe lamp filament monitoring circuit comprising,

a. transformer means having a primary and a secondary winding,

b. an a.c. signal source connected to said primary winding,

c. a lamp filament connected in parallel with said secondary winding,said transformer means supplying electrical energy to said lampfilament,

d. monitoring means having a first and a second state connected in saidprimary winding of said transformer and responsive to the current insaid primary winding of said transformer, said monitoring meansinitially in said second state,

e. auxiliary loading means connected in parallel with the secondarywinding of said transformer means and effective to increase power flowthrough said primary winding of said transformer means.

3. The fail-safe filament monitoring circuit as described in claim 1,wherein said monitoring means is a current responsive electromagneticmeans.

4. The fail-safe filament monitoring circuit as described in claim 3,wherein said electromagnetic means is a current responsive relay.

5. The fail-safe filament monitoring circuit as described in claim 1,wherein said auxiliary loading means is a resistive device.

1. A fail-safe lamp filament monitoring circuit comprising, a.transformer means having a primary and a secondary winding, b. an a.c.signal source connected to said primary winding, c. a lamp filamentconnected in parallel with said secondary winding, said transformermeans supplying electrical energy to said lamp filament, d. monitoringmeans having a first and a second state connected in said primarywinding of said transformer and responsive to the current in saidprimary winding of said transformer, said monitoring means initially insaid second state, e. auxiliary loading means connected in parallel withthe secondary winding of said transformer means and effective toincrease power flow through said transformer means to energize saidfilament to a preselected energizing power flow level where saidmonitoring means assumes and is held operated in said first state atsaid energizing power flow level, said monitoring means resuming saidsecond state at a preselected lower current flow level of said primarywinding of said transformer means when said filament is no longerenergized.
 2. The fail-safe filament monitoring circuit as described inclaim 1, wherein said preselected lower current flow level is due to themagnetizing current of said primary winding of said transformer means.3. The fail-safe filament monitoring circuit as described in claim 1,wherein said monitoring means is a current responsive electromagneticmeans.
 4. The fail-safe filament monitoring circuit as described inclaim 3, wherein said electromagnetic means is a current responsiverelay.
 5. The fail-safe filament monitoring circuit as described inclaim 1, wherein said auxiliary loading means is a resistive device.